On
the path to a virtual violin, musician creates the
vBow

In the
never-ending rhapsody of musical innovation, the vBow
sounds a small but significant note.

Invented
by Charles Nichols, a doctoral candidate in computer
music theory and acoustics, the virtual violin bow
resembles its traditional counterpart only in
passing. A fiberglass rod moves back and forth
through a hole at the end of a robotic arm, which is
connected to an acrylic base shaped like a violin.

Yet this
contraption, which uses servomotors and encoder
sensors instead of strings, acts and sounds like a
real violin bow does on real violin strings. By all
accounts, Nichols, 34, is the first person to have
developed a virtual stringed instrument that employs
haptic feedback, allowing the musician to actually feel
as though he is playing a violin.

The vBow
also is Nichols' first step toward developing a
computer-music instrument he can play as violinist.
Once completed, the virtual violin, or vViolin, will
allow him to produce computer music that is more
expressive than that of a MIDI (musical instrument
digital interface) violin. The vViolin also will
allow Nichols to produce a vast range of sounds --
such as those of a trumpet or double bass, to cite
two conservative examples -- but by using violin
motions and technique.

"This
work came out of my work as a violinist and composer
trying to write interactive computer music that was
expressive for a performer and rich in timbral and
dynamic contrast," Nichols explained the other
day, sitting in a trailer office behind the Center
for Computer Research in Music and Acoustics. On the
wall behind him hung a series of vBow bases staggered
from left to right -- from earliest to more recent --
like a depiction of evolutionary man.

"I
decided to develop an instrument I could play as a
violinist," he added. "I don't have to play
a keyboard, and I don't have to play a wind
controller, and I don't have to try to get MIDI to
sense what I'm doing."

Nichols,
who earned a bachelor's degree in violin performance
from the Eastman School of Music and a master's
degree in music composition from Yale, initially set
out to use a MIDI violin for his compositions, but
found it wanting in several ways. The MIDI violin
works by transmitting information about how violin
strings vibrate to a digital synthesizer, which uses
software to reproduce the sound. The system is
unresponsive and prone to error, Nichols said. For
one thing, there's often a substantial delay between
the time a string is bowed and its vibration is
translated into MIDI pitch and velocity information,
he said. This results in a gap between the
performance gesture and the sound, and rapid changes
in bow direction and pitch often are not translated.

So
Nichols set out to build a violin that did not depend
on MIDI but instead sent data almost instantaneously
from multiple sensors into a computer. "The vBow
has really good resolution, which means that it
senses really accurately all of my motions," he
said. "So you can hear that as I draw the vBow
at a regular speed, I get a clear violin sound. But
if I draw the vBow too quickly, you can hear that
it's as if the bow is skimming over the top of the
string and just playing the higher partials or
frequencies of the sound. And if I draw the vBow too
slowly, it's as if the bow doesn't get the string to
vibrate."

Haptic
feedback has been used extensively by scientists
experimenting with virtual reality and robotics.
Technology magazines these days are filled with
pictures of people wearing futuristic-looking gloves
to control a robotic arm, which, when it closes its
metallic fingers around an object, will communicate
the resistance of that object back to the
glove-wearer.

For
musicians, the feeling of an instrument is key to
their ability to express a note in a particular way.
Witness, say, the dramatic antics of Geoff Nuttall, a
violinist with the St. Lawrence String Quartet
(Stanford's ensemble-in-residence), or the
contortions of a jazz pianist trying to hit a chord
in just the right way. A musician's rapport with his
instrument is intimately physical.

"An
electronic instrument that doesn't take into account
how the player responds to the feeling of playing it
is really missing half the interface," Nichols
said. "Originally, the vBow was going to be an
instrument that just used sensors to track my bow
position, but then I learned about haptic feedback.
So as you're moving the bow back and forth, you can
feel a vibration and friction; as you're moving the
bow in rotation across the virtual strings, you can
feel the détentes of the string crossings; and as
you're moving vertically into the string, you can
feel the elasticity -- the springiness -- of the
strings."

Nichols
still has a way to go before his vViolin is
completed. For one thing, he has yet to develop the
vStrings for controlling pitch (although he has
already built the fingerboard). He also must
construct the vBody. These projects, he predicts,
will take a few years.

Meanwhile,
he will begin work at the end of the month as an
assistant professor of composition and music
technology at the University of Montana, where he was
hired in July.